Geochemical and palynological investigation of the Shengli River marine oil shale (China): Implications for paleoenvironment and paleoclimate

The Shengli River oil shale, located in the North Qiangtang depression, northern Tibet plateau, represents a potential large marine oil shale resource in China. A geochemical and palynological investigation of the oil shale was performed to reconstruct paleoenvironment and paleoclimate during deposition. The total organic carbon (TOC) contents (15.05%–20.34%) and S2 values (103.27–129.12 mg HC/mg rock) of oil shale samples are high, and the organic matter consists mainly of type II kerogen. The thermal maturity assessed from PI (0.033–0.036) and Tmax (433–436) shows an immature to early mature stage of the organic matter. Analyzed oil shale samples from the Shengli River area are characterized by a dominance of low carbon number molecular compositions with high C21−/C21+ (2.10–2.83), low Pr/Ph (0.63–0.75) and high concentrations of C27 sterane and homohopanes (C31–C35), indicating reducing environments, highly saline conditions, and a prevalent contribution of algae to organic matter accumulation. The analyzed oil shale samples have an uncommonly heavy C isotopic composition, ranging in δ13C values of bulk organic matter from − 20.79‰ to − 21.78‰. The enrichment in 13C is mainly attributed to the high productivity of algae rather than solely the result of hypersalinity.Composition of palynofloras from oil shale samples suggests that the climate of the Qiangtang basin region during the deposition of oil shales was warm and humid or sub-humid.